B, as far as we know humans aren't from space
Answer:
Primary succession is the orderly and predictable series of events through which a stable ecosystem forms in a previously uninhabited region. Primary succession occurs in regions characterized by the absence of soil and living organisms.
Geologists have divided the earth history into time units that are largely based on the earth's biotic composition. The modern geological time scale includes both relative and absolute age dating and represents the most up-to-date assessment of the earth's history.
In the modern geological time scale, the eras in earth's history when the planet was populated with advanced life forms are referred to as the Paleozoic (meaning ancient life), the Mesozoic (meaning middle life), and the Cenozoic (meaning recent life).
An observation that increases or decreases consistently in response to a changing variable is a trend. A trend shows the rate something increases or decreases due to a changing variable.
I hope this helps!
<em>~kaikers</em>
Answer:
- Cell mediated immunity uses what type of WBC to attack and kill the infected cell? <u>T-cells</u>
- <u> Helper T </u>or <u>Killer T cells</u> are released that cause the cell to lyse or <u>undergo apoptosis.</u>
Explanation:
White blood cells or leukocytes are integral to cell-mediated immune function in the human body. T cells are produced in bone marrow, and mature in the thymus. They recognize antigens on virus-infected cells and target them for attack; antigens and receptors fit together to allow for identification.
- Helper T cells aid in activating other immune cells, along with eliminating cells infected by pathogens; they release cytokines
- Killer T cells produce special toxins (perforins and then cytotoxins) that lead to cell lysis and programmed cell death or apoptosis.